Mammography has long been used to screen for breast cancer and other abnormalities and for diagnostics. Traditionally, mammograms were formed on X-ray film, but more recently flat panel digital imagers have been introduced that acquire a mammogram in digital form and thereby facilitate analysis and storage and provide other benefits as well. Further, substantial attention and technological development has been dedicated towards obtaining a three-dimensional image of the breast, using methods such as breast tomosynthesis. In contrast to the 2D images generated by legacy mammography systems, breast tomosynthesis systems construct a 3D image volume from a series of 2D projection images, each projection image obtained at a different angular displacement of the x-ray source relative to the image detector as the x-ray source is scanned over the detector. The constructed 3D image volume is typically presented as a plurality of slabs or slices of image data, the slabs geometrically reconstructed on planes parallel to the imaging detector. The reconstructed tomosynthesis slices reduce or eliminate the problems caused by tissue overlap and structure noise in single slice two-dimensional mammography imaging by permitting a radiologist to scroll through the slabs and view underlying structures.
Tomosynthesis systems have recently approved for breast cancer screening and diagnosis. The assignee of this patent specification, Hologic, Inc., has demonstrated at trade shows in this country a fused, multimode mammography/tomosynthesis system that takes either or both types of mammogram and tomosynthesis images, either while the breast remains immobilized or in different compressions of the breast. Other companies have proposed the introduction of systems which are dedicated to tomosynthesis imaging, i.e., which do not include the ability to also acquire a mammogram.
Restricting systems to tomosynthesis acquisition and image display may present an obstacle to acceptance of the tomosynthesis imaging technology, as medical professionals have grown accustomed to screening and analysis of mammogram images. Mammograms offer good visualization of micro-calcifications, and can offer higher spatial resolution when compared with tomosynthesis images. While tomosynthesis images provided by dedicated breast tomosynthesis systems in the art have other desirable characteristics (i.e., better visualization of structures), such systems do not leverage the existing interpretation expertise of medical professionals.
One method of leveraging existing medical expertise to facilitate the transition to tomosynthesis technology was described in U.S. Pat. No. 7,760,924, entitled “System and Method for Generating a 2D Image from a Tomosynthesis Data Set.” The '924 patent describes a method of generating a synthesized 2D image which may be displayed along with tomosynthesis projection or reconstructed images, to assist in screening and diagnosis.